Telephone system



March 26, 1940. w. H. MARTIN 2,195,3

- TELEPHONE SYSTEM Filed Feb. 24, 1939 T0 CON/V.

IN l/EA/TOR Wh! MART/N ATTORNEY Patented Mar. 26, 1940 PATENT, OFF-ICE TELEPHONE SYSTEM William H. Martin, Ohappaqua, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 24, 1939, Serial No. 258,133

11 Claims.

This invention relates to telephone systems and particularly to those systems in which automatic switches are used for establishing connections.

The object of the invention is to eliminate some of the individual equipment usually provided for subscribers lines, especially the line and cut-ofi relays.

It has been proposed heretofore to eliminate the individual line relays and to replace them by a relay mechanism common to a group of lines.

To accomplish this, however, it would be necessary to provide an auxiliary switching mechanism for associating the common relay mechanism with any one of the lines when calling.

It has also been proposed to use a vacuum tube in common to a group of lines, the control element of which is connected through individual resistances to the respective subscribers lines, thus doing away with the individual line relays, and to utilize the vacuum tube as the signaling means for starting the line-finder switch that is to be used for connecting with the terminals of the calling line. An arrangement of this kind, however, is subject to false operation due to the combined effect of several line leaks, and further does not lend itself readily to a line terminal test which is sumciently positive and reliable to enable the line finder to distinguish and seize the particular calling line in the group that is calling.

According to the present invention these dlfllculties are overcome by the use of three gaseous conductor tube devices having single control electrodes two of which are inductively coupled to the group of lines to produce an impulse when a line calls that will alter the potential of one of the control electrodes so as to render the. associated tubeconducting and thereby establish an anode-cathode circuit therethrough which, in

turn, will initiate the operation of a line-finder switch that will hunt for the test terminal of the calling line.

Another feature of the invention is a testing arrangement in which the closure of the line loop at the substation places a potential on the corresponding line test terminal accessible to the hunting finder switch simultaneously with the alteration of the control electrode potential of one of the tubes. This calling potential on the test terminal of the calling line permits the switch, in hunting for said line, to discriminate between it and the idle lines of the group since the calling condition on the terminal of the line that initiates a call does not manifest itself on the terminals of any of the idle lines in the group.

The foregoing and other features of the invention will be described in detail in the following specification which should be read in conjunction with the attached drawing and accompanying claims.

The drawing represents, schematically, a telephone system in which the features of the invention are embodied in a circuit structure that makes use of automatic switches of the wellknown two-motion step-by-step type. It is understood, however, that the embodiment of the invention as herein set forth is given by way of illustration only, and that the invention may be readily applied to any other type of automatic or semiautomatic telephone system.

Referring to the drawing, there are shown two subscriber stations of a group of twenty lines, namely, stations A and D in the group, a line circuit LC associated with station A, a linefinder switch LP, a selector switch S, a connector switch C, and a called subscriber's station B.

The subscribers stations A and D are provided with the usual subscriber's set which is equipped with a dial for controlling the establishment of the desired connections. The selector switch S and the connector switch C are of the well-known step-by-step or Strowger type, and reference may be had to pages 53 to 67, inclusive of the second edition of Automatic Telephony" by Smith and Campbell for a detailed description of the operation of the circuits associated with these switches. Only those portions of the circuits of the selector and connector switches are shown as are required for a clear and complete description of this invention, the omitted portions of these circuits being indicated by broken lines.

The line circuit LC and the line-finder switch LF are shown in detail since the features of the invention apply specifically to these circuits. Three cold cathode gaseous discharge tubes T1, T2, T3 are associated in common with a group of line circuits such as those associated with the group of stations AD, for example, the control electrode 4 of tube T1 and the control electrode 3 of tube T2 being connected in parallel to the secondary winding S of transformer 9 through suificiently positive with respect to the potentials of their associated cathodes. Each individual line circuit of the group, such as line circuit LC. connects with the primary side P of transformer 9 over one line conductor through individual resistances such as, for instance, resistances 42 and 4| for subscriber's line A. The mid-point connection between the two resistances is connected to the test terminal 23 of the line in the bank of terminals accessible to the line-finder switches, such as switch LF.

As already stated, the control electrode 3 of the second tube T2 is further connected to the secondary S of transformer 9 by way of series condenser l8 and its associated resistance while the cathode 5 of the first tube T1 is connected directly to the segment on the commutator which designates the horizontal lever of the line group controlled by the tubes T1, T2 and T3, and through resistance 31 to the winding relay l2 via the No. 4 normal contacts of relay 38 in the preferred line finder LF, and also to the control electrode 3 of tube T2 through resistance l3, to the control electrode M of tube T3 through condenser 29 and resistance 28, and to the source of positive power supply 24 through condenser 29 and resistance 21.

Each line circuit connects to a set of three terminals appearing in the terminal banks accessible to a group of line-finder switches, as indicated by the individual line circuit LC which connects to terminals 2|, 22 and 23. The linefinder switch LF is of the well-known step-bystep type provided with two banks each of hundred'sets of terminals of which the upper bank of one hundred terminals is typically represented by the terminals 2|, 22 and 23 and the lower bank of one hundred terminals by terminals 3|, 32 and 33, said last group of terminals being located in a levelcorresponding to the level which holds the first group. The two banks of terminal sets are arranged in ten levels, each level consisting of ten horizontal terminal sets, the upper bank sets being selectable by brushes l5, l6, l1 and the lower bank sets by l5, l6 and I1. These brushes, as well as brush 8, are carried on a common shaft (not shown) which is advanced vertically to the proper level and then horizontally to the terminals of the calling line under control of the vertical magnet II for vertical stepping and the rotary magnet 20 for horizontal stepping,

respectively. The line finder is provided with a vertical commutator 1 which has ten conducting segments, one for each two levels of terminals in similar horizontal disposition in each of the two terminal banks. Associated with this c'ommutator is a brush 8 which, as stated before, is mounted on they common brush shaft and advances simultaneously with brushes l5 to II, inclusive, and 5 to IT, inclusive during vertical stepping to engage the successive segments ofthe commutator.

The operation of the circuits controlling the setting of a connection will now be full set forth in detail in the following description of a call initiated from station A for termination at station B.

When the receiver is removed from the switchhook at station A to originate a call, a circuit is completed from ground through the primary winding P of transformer 9, conductor 40, resistances 4| and 42, loop of station A, resistance 43, positive battery to ground. During the build-up of current in this path, a momentary surge of potential is induced in the transformer coupled path which may be traced from ground through the secondary winding S of transformer 9, condenser 6, and associated resistance, resistances 30 and 35 to positive battery 24, and in parallel therewith through resistances 34 and III to negative battery 36. Control electrode 4 of tube T1 is normally at a positivebias. This is because the potentiometer resistances 35, 34 and ID are so calculated as to place a "critical" positive potential on electrode'4 but not sufficient to fire the tube unless a positive impulse is produced through the transformer 9 or tube T3 is conducting as will be explained later. Control electrode 3 of tube T2, on the other hand, has no bias of any kind since its control electrode 3 is connected, through resistance l3, to the cathode battery of tube T1, and will not be able to fire unless such electrode is rendered positive. Hence when the impulse is produced through the transformer, the potential of electrode 4 is raised to the flash point of the tube, causing it to break down between control electrode 4 and cathode 5, after which a current is established between cathode 5 and anode l9, over the following path: positive battery 24, anode l9, cathode 5, resistance 31, conductor 55, No. 4 normal contacts of relay 38, winding of relay l2, No. 3 contacts of relay 39 to negative battery. Relay l2 operates and performs functions noted hereinafter. The full potential drop in resistance 31 and relay winding 2 is further applied to terminal 8 of the vertical marking commutator 1, thus indicating that the calling line is in the group of lines located on the eighth level of terminals either in the upper set or lower bank of terminals.

It will be observed that the inductive surge through transformer 8 is also applied to the control electrode 3 of tube T: but that this electrode has no positive bias as in the case of the control electrode of tube T1. Hence the positive potential created by the surge will not be sufficient to render the control electrode positive enough to cause tube T: to break down. However, when tube T1 has broken down in the manner already described, the potential drop in the resistance 31 and relay winding I2 is available as a positive bias voltage between the control electrode 3 and cathode 60 of tube T2, through resistance l3; That is to say, tube T2 now has acquired a positive bias on its control electrode 3 so that a second impulse produced through the transformer 9 will have the effect of rendering control electrode 3 sufiiciently positive to cause tube T2 to break down and perform functions hereinafter described.

Assume that terminals 2|, 22 and 23, associated with the line circuit LC of calling station A, are the fifth set of terminals in the eighth level of the upper bank of terminals of the line-finder switch. Tubes T1, T2, and T3 are common to all of the twenty lines appearing in the eighth level of each of the two terminal banks, each of these lines connecting with the control electrodes of the first two tubes through the secondary of transformer 9 as previously explained. Upon the aforementioned breakdown of the tube T1, in response to the initiation of the call at station A, a potential is placed upon the eighth segment of commutator 1 and relay I2 is operated as previously described. Relay l2 grounds the sleeve lead 44 to the selector S at its upper inner contacts, and closes a circuit for relay 45 extending from ground on the No. 3 contacts of relay [2, contacts of vertical magnet contacts of rotary magnet 20, lower winding of relay 45, to battery on the No. 3 contacts of relay 33. Relay 45 oper- 76 areas" ates and closes the circuit of verticalmaznet II from battery on the No. 3 contacts of relay 33,

winding of vertical magnet II, No. 4 back con-- tacts of relay 46, contacts of relay 45 to ground on the lower contacts of relay l2. Vertical magnet ll operates and lifts the brush shaft one vertical step to the first level of terminals and breaks its own contacts to release relay 45 which in turn opens the driving circuit of the magnet which, on releasing and closing its contacts, re-'- establishes the circuit of relay 45 and the consequent reestablishment of that of magnet II which operates to lift brush shaft to the second level of terminals. These operations and circuit interruptions continue until the shaft has been lifted to the eighth terminal level in which the calling line is to be found, as is evidenced by the presence of the potential from cathode 5 of tube T1 on the eighth segment of the commutator 1. When this segment is reached, a circuit is completed for relay 46 in series with lower winding of relay 45, which circuit extends from positive battery 24, anode l9 and cathode 5 of tube T1, eighth commutator segment,brush 8, upper winding of relay 46, outer contacts of rotary magnet 20, lower winding of relay 45, No. 3 contacts of relay 38 to negative battery. Relay 46- operates, locks over its lower winding to ground on the contacts of relay I2, and further holds relay 45 operated to prevent further vertical stepping. Relay 46 transfers the locking circuit of relay 41 from the off-normal ground on the vertical off-normal contacts VON, which operates on the first vertical step of the brush shaft, to a circuit path which is partially completed at every rotary step, as subsequently set forth, through the No. 1 operated contacts of relay 46, inner contacts of rotary magnet 26, contacts of relay 45 to ground on the lower contacts of relay l2. Relay 46 is made slow in operating to provide a short interval between the last vertical step and the first rotary step in order to prevent the brush wipers from snagging because of vibration. Relay 46 also transfers the stepping circuit from the vertical magnet II to the rotary magnet 20 oyer the following path: battery, through the winding of rotary magnet 20, No. 4 front contacts of relay 46, contacts of relay 45 to ground on the lower contacts of relay l2. The rotary magnet 20 now steps the brush shaft around on the eighth level terminals (causing thereby the disengagement of brush 8 from the eighth commutator segment), and, on the first step, effects a release of relay 45 because the disengagement of brush 8 with the eighth segment of commutator I and opens thepreviously traced holding circuit through the operating winding of relay 46. Relay 45 now reoperates over the previously traced circuit, in turn causing the operation of rotary magnet 20 to effect a second step of the brush shaft, these operations continuing until brush l1 engages terminal 23 of line A, distinguished from all other similar terminals of the level by the presence thereon of a potential produced by battery through resistance 43, line loop and resistance 42 as previously described.

It will be observed that two other gaseous con: ductor tubes 13-! and Fl are provided, the anodes of which are paralleled to the positive direct current superimposed upon the source of alternating current 49, while the control electrode 49 of tube 3-! is connected to the upper test brush l1 through current limiting resistance 53 and the control electrode 56 of tube F-I is connected to the lower test brush l1 through contacts of relay l2.

current limiting resistance 54. The cathodes II and 52, respectively, of both tubes are kept at ground potential so that neither tube is in a conducting state so long as its control electrode is not rendered positive during the positive halfcycle of the alternator 48. However, when test brush l1 engages terminal 23 of the calling line A, the positive potential on this terminal is applied to control electrode 49 of tube B-l via resistance 53. Since cathode 5| is at ground v potential, the potential difference between cathsaid potential would then be applied via resistance r 54 to control electrode 50 of tube F-I. Since cathode 52 of this tube is also kept at ground potential, the potential difference between control electrode 50 and cathode 52 would cause tube B-| to break down and become conducting.

Assuming, however, that the calling line is line A, located in the upper bank, then the engagement of brush l1 with terminal 23 results in tube 3-! becoming conducting, whereupon a circuit is completed for relay 41 in series with the upper winding of relay 45, extending from positive potential at cathode 5|, lower winding of relay 41, No. 5 back contacts of relay 39, No. 5 normal contacts of relay 41, upper winding of relay 45 to ground on the No. 2 contacts of relay I2. Relay 41 operates, at least to the extent of closing its No. 2 contacts.

Since relay 46 is operated and rotary magnet 20 is held through the No. 4 front contacts of said relay to ground on the lower contacts of relay l2 via the contacts of relay 45, the full operating and locking circuit of relay 41 is completed over the inner contacts of rotary magnet 29, contacts of relay 45 to ground on the lower It is necessary to insure a fast auxiliary circuit to completely energize relay 41 because when alternator 48 reaches the negative half-cycle, the anode of tube 3-! becomes negative and the tube extinguishes, thereby opening the initial operating circuit of relay 41. A circuit is now completed for relay 39, extending from battery through its lower winding, No. 3 contacts of relay 41, inner contacts of magnet 20, contacts of relay 45 to ground on the lower contacts of relay l2.

Note that if line D had initiated the call instead of line A, the calling potential would be present, of course, on terminal 33 instead of terminal 23 and tube F-l would have been rendered conducting instead of tube B-|. Under these assumed circumstances, relay 41 would not operate but relay 39 would in a circuit completed from the positive potential available at cathode 52, upper winding of relay 39, No. 1 back contacts of relay 38, upper winding of relay 45 to ground on the No. 2 contacts of relay l 2. operating, would then lock over its lower winding through the circuit path already described.

The operation of relay 39 extends the talking conductors from the No. l and No. 4 front contacts of relay 41, over its own No. 1 and No. 6 contacts, respectively, to the selector S, opens the initial circuit of relay 41 at its No. 5 back con- Relay 39, upon tacts, closes a circuit for relay 38 which extends from battery through its upper winding, No. 2 front contacts of relay 39, to ground on the lower operated contacts of the vertical off-normal contact set VON, opens the circuit of relay l2 at its No. 3 contacts, and further opens the negative battery supply, through the winding of relay l2 and resistance 31, to the cathode 5 of tube T1,

which causes the tube to become non-conducting except under certain conditions to be described later. Relay l'2 releases, disconnects ground from the upper winding of relay 45, causing it to release, in turn releasing relay 46. The operation of relay 38 joins sleeve brush I I of the line finder LF to sleeve conductor 44 of the selector S over the No. 1 front contacts of said relay and the No. 5 alternate contacts of relay 4! extends the locking ground of relay 39 to said conductor 44 over its N0. 2 contacts, advances the starting conductor 55 to relay l2 in the next succeeding idle line-finder switch in the chain over its No. 4 front contacts, and removes battery from relays 45 and 46 and vertical magnet ll. Relay 38 further connects alternating potential source 51 superimposed on negative battery to conductor 55 which connects with the cathode 5 of tube T1. Since the effect of this is to connect negative potential to the cathode 5 on every half-cycle of the alternator 51, then on the positive portion of the wave, cathode 5 is rendered positive. Should another line in the group now initiate a call, tube T1 will break down by virtue of exactly identical circuit conditions established through relay 12 of the succeeding line finder by the operation of relay 38. However, while the succeeding line finder is hunting for the calling line, the tube T1 will remain conducting because of the cathode-anode circuit heretofore described but now through the winding of relay (2 of the succeeding line finder. There will be, in addition, a flow of pulsating current from the superimposed sources 51 through the lower winding of relay 38 which will prevent this relay from releasing while relay l2 in the succeeding line finder is operated. However, when the circuit through relay I2 is opened in the succeeding line finder as described for the line finder shown in the drawing, pulsating current will continue to fiow through both relays 38 to the cathode 5 of tube T1 which will then become non-conducting in the negative half-cycle after relay l2 in the succeeding line finder has released.

The calling line A is nowv extended to the first selector S which is then positioned on the terminals of an appropriate connector C by one series of dial impulses, the connector itself being then positioned on the terminals of the called station B by the next two series of dial impulses transmitted from the dial atstation A, all in accordance with well-known automatic telephone practice. as the release of the connection forms no part of this invention, further description thereof is omitted.

If a second line in the group of twenty lines attempts to initiate a call after a previous line has caused tube T1 to become conducting but before the line-finder operations above described have been completed, the second positive impulse from the surge through transformer 9 will cause tube T2 to break down and become conducting because of the presence of the positive bias on the control electrode 3 of tube T2 as previously described. Note that unless tube T1 is conducting, the surge voltage from transformer 9 would Since this part of the operation as well 1 not cause tube T2 to break down. Tube T: is,

maintained conducting over a cathode-anode circuit extending from positive battery 24, anode GI and cathode 68, resistance 2 to negative battery 36. The potential drop in resistance 2 applies a critical positive bias to control electrode l4 of tube T3 via resistance 82 and resistance 28. Now when tube T1 becomes non-conducting as a result of the operation of relay 39, a positive inductive surge from the winding of relay l2 and that inherent in the internal inductance of tube T1 will be applied to the control anode l4 of tube Ta via condenser 29 and resistance 28 causing said tube to break down and become conducting. Tube T2 is now extinguished by the positive surge applied to its cathode 80 through the commutating condenser 59. But when tube T3 is conducting, the potentiometer formed by resistances 34 and 35 together with the voltage drop in resistance l applies a positive voltage to the control electrode 4 of tube T1. This voltage, however, is not applied immediately, but only after a delay as required by the charging time of condenser 58 through resistance 34. This delay is introduced to allow time for the operation of relay 38 after the operation of relay 39. The potential thus applied to control electrode 4 of tube T1 will cause it to break down again to initiate the operation of the next succeeding line finder via conductors 55 and 56. When tube T1 thus reoperates it extinguishes the discharge in tube T3 by means of the commutating condenser connected between the cathode of tube T1 and the cathode 65 of tube T3. now in the same condition as that existing just after a single subscriber such as A has initiated a call and the operations are the same as those described.

While this embodiment of the invention has been described with reference to a line-finder' system in which there are three tubes to accommodate the satisfactory initiating of two overlapping calls in the same group of lines, it is evident that the tube counting circuit could be adapted to store as many overlapping calls as might be required by the provision of additional tubes similar in function to tubs T2.

What is claimed is:

1. In atelephone system, a switch, magnet means for setting said switch, a gas-filled tube, and inductive means for rendering said tube conductive to operate said magnet means for setting said switch.

2. In a telephone system, the combination with a line and a connecting means therefor of a gaseous conductor device inductively coupled to said line whereby the initiation of a call by said line produces an impulse surge that renders said device operative to effect a connection of said connecting means to said line.

3. In a telephone system, the combination with a line, a source of potential connected therewith and connecting means therefor, of a gaseous conductor device inductively coupled to said line through said source of potential whereby the initiation of a call by said line produces an inductive surge that renders said device operative to effect a connection of said connecting means to said line and a steady current flow that produces a distinctive line test potential to which said connecting means responds in eifecting said connection.

The circuit is I 4. In a telephone system, the combination with arcasrr trode or which is inductively connected to said line and the cathode-anode space discharge circuit 01 which is operatively associated with said,

connecting means whereby the initiation of a call from said line produces an inductive surge that makes said control electrode positive and renders said device conducting through its space discharge circuit to effect a juncture of said connecting means with said calling line and means operative subsequent to the juncture of said connecting means with said calling line for disrupting said space discharge circuit to reset said device.

5. In a telephone system, the combination with a group oi lines and connecting means therefor oi a gaseous conductor device inductively cou-- pled to said group of lines, means whereby the initiation of a call by any line in said group produces an impulse that renders said device operative to efiect a connection of said connecting means to said calling line.

6. In a telephone system, the combination with a group of telephone lines and connecting means therefor, of a gaseous conductor device the control electrode oi which is inductively connected to said line and the cathode-anode space discharge circuit of which is operatively associated with said connecting means whereby upon the initiation of a call from one of said lines said control electrode renders said device conducting through its space discharge circuit to eflect a juncture 01' said connecting means with said calling line and means operative subsequent to the juncture of said connecting means with said line for disrupting said 'space discharge circuit to reset said device.

7. In a telephone system, a group 01' lines disposed upon the terminals a line-finder terminal bank, a line-finder switch adapted to hunt over said terminals, a gaseous conductor tube having a control electrode, a cathode and an anode, an inductive connection between said group of lines and said control electrode whereby upon the closure of one 01' said lines to initiate a call the surge of potential created through said inductive connection electrically ail'ects said control electrode to render said tube conducting, and a cathode-anode circuit for said tube responsive to the conduction of said tube for initiating the operation of said line-finder switch to hunt over the terminals or said terminal bank in search of said calling line.

8. In a telephone system, a group of lines disposed upon the terminals of a line-finder terminal bank, a line-finder switch adapted to but over said terminals, a gaseous conductor tube having a control electrode and a cathode-anode circuit,

an inductive coupling device disposed between I said group or lines and the control electrode oi said tube whereby a surge created through said device in response to one or said lines initiating a call renders said control electrode positive to cause said tube to become conducting in its cathode-anode circuit. and means in said cathodeanode circuit responsive to the conductive condicharge circuit that includes an element of said.

line-finder switch whereby said control electrode is made positive by the inductive surge produced in response to a line in the group initiating a call to render said tube conducting through its cathode-anodecircuit for operating said line-finder element to initiate the operation of said lineflnder switch to hunt for the terminals of said calling line, and whereby said control element is not aiiected by leakage currents flowing through the network formed by the lines through their separate sources of potential and the inductive coupling of the control electrode.

10. In a telephone system, a plurality of subscriber line loops each subject to leakage paths and each having a source of potential, a line finder having access thereto and astart circuit for said line finder comprising an electromagnetic device, a gas-filled tube having an anode, a cathode and a control electrode, a transformer and another source of potential, the primary winding of said transformer being connectable in parallel with all of said line loops including their respective sources of potential, and the secondary thereoi being connected to the control electrode of said tube, and a circuit for said electromagnetic devic'e extending from said other source of potential over the cathode-anode path of said tube,

said tube being ionizable by the closure of any one of said line loops to operate said device by the inductive surge produced through said transformer but not responsive to leakage paths in said line loops.

11. In a telephone system, a group of lines including a source of potential and a resistance for each line terminating on the terminals of a lineilnder bank, a line-finder switch adapted to hunt over said terminals, a gaseous conductor device having a control electrode and a cathode-anode space discharge circuit path including serially therewith an electromagnetic device for said linefinder switch, means for inductively coupling said control electrode to said lines, said means including a circuit completing path for each line source oi potential through its associated resistance and its associated line whereby upon the initiation of a call from any line an inductive surge alters the potential of said control electrode to render said tube conducting in its cathodeanode space discharge circuit, and whereby said electromagnetic device is operated to start said line-finder switch to hunt for a terminal of said calling line as marked by the potential thereon produced by the current flow through the line resistance.

WIILIAM H. MARTIN. 

